The solid-borne sound signal that is used for knock control in a combustion engine varies considerably in amplitude over the entire load and rotation-speed range of the combustion engine, because of changes in the engine's baseline noise. The solid-borne sound signal is sensed by a knock sensor, which outputs a sensor signal that is very small (usually a few mV) in the rotation speed range close to idle, and is in the range of, for example, a volt at full load and rated speed. Signal evaluation of the sensor signal is accomplished in a control unit; in order to evaluate the sensor signal, the control unit must ensure that in the low-signal range, the sensor signal is still resolved with sufficiently high accuracy that it can be filtered. In addition, in the high-signal range the sensor signal should require only part of the available evaluation range, so that knocking combustion events, which are detected as a sensor signal amplitude that is elevated with respect to the baseline signal level, do not exceed the detection range for signal evaluation, with the result that signal components important for knock detection would be lost.
In order to ensure sufficient resolution over the entire amplitude range of the solid-borne sound signal, the sensor signals of the knock sensor are amplified or not amplified as a function of the magnitude of the solid-borne sound signal and as a function of the rotation speed of the combustion engine. Gain control of this kind amplifies the voltage signals when the solid-borne sound signals are small, and processes the voltage signals neutrally when the solid-borne sound signals are large.
The document DE 10 138 110 A1 discusses a method and an apparatus for knock detection and knock control, in which a sensor signal of a knock sensor is delivered to an amplifier and amplified therein in accordance with the need for further evaluation. The amplified signal is forwarded to an adjustable bandpass filter by selecting a frequency band in which the frequencies characteristic of knocking are located. Interference signals that are located in a different range can be effectively blocked out as a result of this bandpass filtration.
Adjustable amplifiers that make available two or more different gain factors, in order to amplify the sensor signal into an optimum signal-level range for signal evaluation in an analog/digital converter, have hitherto been provided for adaptation of the sensor signal. Implementing an adjustable amplifier of this kind for the analog sensor signal using discrete circuit technology is, however, complex and error-prone, in particular when two or more gain factors need to be implemented.
It is therefore an object of the exemplary embodiments and/or exemplary methods of the present invention to make available a knock detection system as well as a method for furnishing an amplified sensor signal of a knock sensor for operating a knock detector system, the outlay for implementing the amplifier for amplifying the sensor signal of the knock sensor being reduced. A further object of the exemplary embodiments and/or exemplary methods of the present invention is to make available a method for furnishing an amplified sensor signal with which a knock detection system of this kind can be operated.